Safe and reliable transabdominal fetal oximetry

ABSTRACT

Systems and methods are described, and one method includes determining a fetal blood oxygenation level, including: activating at least one light source with at least two distinct wavelengths of light on an abdomen of a pregnant mammal to direct light into a maternal abdomen toward a fetus; receiving a set of mixed signals from a set of photodetectors positioned at different locations on the maternal abdomen from reflected light that traverses maternal tissue or maternal tissue and fetal tissue; determining the fetal blood oxygenation level by performing computations on a composite fetal signal produced from the mixed signals; and ensuring a skin temperature of the maternal abdomen does not rise to unsafe levels due to activating the at least one light source.

This application claims the benefit of priority from U.S. ProvisionalPatent Application Ser. No. 62/941,525 filed Nov. 27, 2019, and entitled“SAFE AND RELIABLE TRANSABDOMINAL FETAL OXIMETRY”, which is incorporatedby reference herein in its entirety.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

This invention was made with Government support under Grant Nos. 1838939and 2015174, awarded by the National Science Foundation. The Governmenthas certain rights in the invention.

BACKGROUND

It is common for intrapartum fetal health monitoring to usecardiotocography (CTG) machines, aka electronic fetal monitors (EFM), tojointly monitor fetal heart and uterine contractions during labor. Arecent improvement for fetal health monitoring provides transabdominal(through the maternal abdomen) measurement of fetus blood oxygensaturation level referred to herein as transabdominal fetal oximetry(TFO), also sometimes referred to as transabdominal fetal pulseoximetry. Transabdominal fetal oximetry (TFO) can potentially improvefetal outcomes by providing physicians with a more objective metric offetal well-being, namely fetal oxygen saturation. TFO technologyinvolves shining near infrared light at several specific wavelengthsinto the maternal abdomen with an optical probe placed on the maternalabdomen, followed by sensing the diffused scattered light. Variations inthe diffused light intensity signal are caused by physiologicaldifferences in tissue composition. The variations in the scattered lightare analyzed to separate fetal information from the raw sensed mixedsignal (mixture of maternal and fetal information). A pulse oximetrycomputation is performed on the isolated fetal signal to estimate thefetal oxygen saturation.

SUMMARY

An important consideration for TFO is to acquire a stronger signalrelative to noise, which requires emitting more and more light into thebody of a pregnant woman. Emitting more light must be balanced withpatient safety (rise in the temperature of the mother's abdominal skin).The disclosure herein provides systems and methods for striking abalance between these two competing requirements to ensure safeoperation of the TFO for intrapartum fetal health monitoring.

A method is disclosed which includes determining a fetal bloodoxygenation level, comprising: activating at least one light source withat least two distinct wavelengths of light on an abdomen of a pregnantmammal to direct light into a maternal abdomen toward a fetus; receivinga set of mixed signals from a set of photodetectors positioned atdifferent locations on the maternal abdomen from reflected light thattraverses maternal tissue or maternal and fetal tissue; determining thefetal blood oxygenation level by performing computations on a compositefetal signal produced from the mixed signals; and ensuring a skintemperature of the maternal abdomen does not rise to unsafe levels dueto the activation of the at least one light source.

A system is disclosed for safely determining a fetal blood oxygenationlevel which includes: at least one light source for positioning on amaternal abdomen of a pregnant mammal to direct light in at least twodistinct wavelengths into the maternal abdomen toward a fetus; acontroller to selectively activate the at least one light source; a setof photodetectors, wherein each photodetector in the set ofphotodetectors is positioned at a different location on the maternalabdomen to receive diffuse reflected light that traverses maternaltissue or maternal and fetal tissue to produce a set of mixed signals; aprocessing mechanism that receives the set of mixed signals and performsa filtering operation to produce a composite fetal signal from the setof mixed signals and determines the fetal blood oxygenation level fromthe composite fetal signal; and wherein the system ensures a skintemperature of the maternal abdomen does not rise to unsafe levels dueto activation of the at least one light source.

A system is disclosed for safely determining fetal health whichincludes: at least one light source on a probe for positioning on amaternal abdomen of a pregnant mammal to direct light in at least twodistinctive wavelengths into the maternal abdomen toward a fetus,wherein the probe includes a temperature sensor that provides ameasurement of the skin temperature of the maternal abdomen; a motionsensor on the probe for detecting motion of the probe to allow motion ofthe probe to be monitored and used to determine signal quality; acontroller to selectively activate the at least one light source; a setof photodetectors in the probe, wherein each photodetector in the set ofphotodetectors is positioned at a different location on the maternalabdomen to receive diffuse reflected light that traverses maternaltissue or maternal and fetal tissue to produce a set of mixed signals; aprocessing mechanism that receives the set of mixed signals and performsa filtering operation to produce a composite fetal signal from the setof mixed signals and determining the fetal blood oxygenation level fromthe composite fetal signal; an electronic fetal monitor that providesmaternal heart rate, fetal heart rate, and uterine contraction signalsthat are used by the processing mechanism to present a unifiedindication of fetal health, wherein the unified indication of fetalhealth includes normal, indeterminate and abnormal fetal health, basedon integration of fetal heart rate tracing and whether the estimatedfetal blood oxygenation level indicates sufficient oxygenation orinsufficient oxygenation; and wherein the system ensures a skintemperature of the maternal abdomen does not rise to unsafe levels dueto activation of the at least one light source by adaptively reducing aduty cycle of the at least one light source. In some embodiments,methods and systems described herein ensure that the skin of thematernal abdomen remains at or below about 44, 43, 42, 41 or 40 degreesCelsius.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Furthermore,the claimed subject matter is not limited to implementations that solveany or all disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures depict one or more implementations in accord with thepresent teachings, by way of example only, not by way of limitation. Inthe figures, like reference numerals refer to the same or similarelements.

FIG. 1 illustrates a high-level diagram of an Integrated IntrapartumFetal Monitor (IIFM) for estimating and monitoring fetal blood oxygenlevels.

FIG. 2 illustrates a block diagram of a signal processing block of theIIFM introduced in FIG. 1 .

FIG. 3 illustrates a functional block diagram of the IIFM introduced inFIG. 1 .

FIG. 4A illustrates a bottom view of an implementation of a probe forestimating and monitoring fetal blood oxygen levels.

FIG. 4B illustrates a cross-sectional side view of an implementation ofa probe for estimating and monitoring fetal blood oxygen levels.

FIG. 4C illustrates a bottom view of another implementation of a probefor estimating and monitoring fetal blood oxygen levels.

FIG. 4D illustrates an enlarged view of an implementation of a lightsource in a probe for estimating and monitoring fetal blood oxygenlevels.

FIG. 4E illustrates a bottom view of another implementation of a probefor estimating and monitoring fetal blood oxygen levels.

FIG. 5 illustrates a flowchart of an implementation of a signal qualityassessor of the IIFM in FIG. 3 .

FIG. 6 illustrates a flowchart of an implementation of skin temperatureprediction in the IIFM in FIG. 3 .

FIG. 7 illustrates a flowchart of an implementation of a fetal healthmonitor of the IIFM in FIG. 3 .

FIG. 8A illustrates an example implementation of fetal heart tracing ofthe IIFM in FIG. 3 .

FIG. 8B illustrates another example implementation of fetal hearttracing of the IIFM in FIG. 3 .

FIG. 9 illustrates a flowchart of an implementation of a safety managerof the IIFM in FIG. 3 .

FIG. 10 illustrates a functional block diagram of an example computersystem upon which aspects of this disclosure may be implemented.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth by way of examples to provide a thorough understanding of therelevant teachings. However, it should be apparent that the presentsubject matter may be practiced without such details. In otherinstances, well-known methods, procedures, components, and/or circuitryare described at a relatively high-level, without detail, to avoidunnecessarily obscuring aspects of the disclosed subject matter.

While the examples and language used focuses on a human female as thematernal abdomen, as used herein, the maternal abdomen may be anymammal. The terms fetus blood oxygenation level, fetus blood oxygensaturation level and fetus hemoglobin oxygen saturation level are usedinterchangeably in this document.

Safety Considerations and Applicable Standards

The safety of emitted near infrared (NIR) light by medical devices withrespect to eye exposure and skin injury are evaluated using twointernational standards IEC 60601-2-57 and IEC 62471, respectively. Bothdocuments are accepted by the Food and Drug Administration as RecognizedConsensus Standards. IEC 60601-2-57:2012 offers specific requirementsfor the basic safety and essential performance of non-laser light sourceequipment used in medical devices. It outlines potential ocular hazardsthat can occur; and suggests exposure limits to protect against thesehazards. It also presents a risk group classification scheme for theassociated device depending on the degree to which ocular hazards arepresent. These limits were designed to protect patients, physicians, andother healthcare staff members from over-exposure (intentional oraccidental) using worst-case scenarios, which provide a conservativesafety limit. Calculated exposure limits for each ocular hazardaccording to IEC 60601-2-57, were compared with the emitted light energyof a device implementing the instant application. The device was belowthe three exposure limits, and it would be classified within the safestrisk group for devices, referred to as the Exempt Group. Note thatnon-coherent light, unlike laser, diverges in all directions and only avery small fraction of the emitted light energy reaches the eye of anobserver.

Potential skin injury due to the thermal effects from infrared opticalradiation was discovered to be an important consideration for TFO. Theinternational standard IEC 62471:2006 provides guidance to manufacturersof light-based systems on the evaluation and control of photo-biologicalhazards and suggests a thermal hazard exposure limit for the skin. Thelimits are based on skin injury due to increases in tissue temperature.The maximum safe skin temperature for long term monitoring is generallythought to be about 42-44 degrees Celsius. Reducing the energy generatedfor continuous TFO monitoring can be accomplished by lowering the lightsource duty cycle as described further below. The duty cycle referred toherein is the percentage of time in which the light sources are on, asthey are quickly turned on and off). Reducing the duty cycle can reducethe exposure to below the limit of the above standards. It is importantto note that light decays exponentially with distance, and thus, thevast majority of emitted light energy is absorbed by, or scatters awayin superficial layers of maternal tissue. The remaining energy, part ofwhich is absorbed by the fetal tissue, is far below safety limits,eliminating concern about fetal safety. In fact, TFO faces the reversechallenge of too little light making it to the fetus. Thus, there is abalance between increasing the light to make sure sufficient lightpenetrates to the fetus, and lowering the light for safety of themother.

This disclosure introduces an IIFM with safety improvements to insurethe maternal abdominal skin temperature does not rise to unsafe levelswith long term use of TFO monitoring. Some implementations may includeat least one temperature sensor on the probe (in contact with the skin)to monitor skin temperature for heat mitigation and/or alarm generationpurposes. Other implementations may include adaptively reducing thestrength of the drive current of the light source emitters to theminimum-required levels based on the sensed signal strength, oradaptively reducing the duty cycle of the light sources to limitadditional light exposure and thereby limit the skin temperature. Yetother implementations may include enhancing convection (air-flow) aroundthe light sources to remove heat, and adding flexible heat sinks incontact with the light sources or the skin to dissipate the heat awayand cool the skin. Other implementations may also collect less frequentmeasurements (e.g., once every 20 seconds) to generate less heat.

FIG. 1 illustrates a high-level diagram of an Integrated IntrapartumFetal Monitor (IIFM) 100 for safely monitoring fetal pulse oximetryusing TFO technology. The IIFM 100 includes a probe 102. The probe 102may be a “wearable” probe that is placed on a maternal abdomen 104 overa fetus 106. The probe 102 is connected to a monitor 114 which istypically placed at a patient's bedside to provide information forhealth care workers. The probe 102 includes at least one light source108. The light source 108 may include one or more light-emitting diodes(LEDs) 110 (not shown) that emit light at one or more distinctwavelengths. A single light source may be used that generates two ormore distinct near infrared wavelengths. Alternatively, multiple lightsources may be used to generate the two or more distinct near infraredwavelengths. Most light sources generate light in a range of adjacentwavelengths (e.g. 800 nm to 820 nm). As used herein, distinctwavelengths are sufficiently separate in the light spectrum and notwithin one narrow range.

As illustrated in FIG. 1 , the light source 108 with the LEDs 110 ispositioned on the maternal abdomen 104 to direct light toward the fetus106. The light source 108 is powered by a drive circuit 112, whichoperates under control of the functional blocks in monitor 114 anddescribed further below. Two or more photodetectors are also positionedin the probe 102 on the maternal abdomen 104. The photodetectorstypically comprise a photodiode. In this example, the photodetector 116receives reflected light 118 that traverses only maternal tissue and inresponse produces a maternal signal to the data acquisition circuit 120.The remaining photodetectors 122 receive reflected light 124 thattraverses both maternal and fetal tissue, and in response produces amixed signal, which include contributions from both maternal and fetaltissue.

Referring again to FIG. 1 , the photodetectors 116, 122 are connected tothe data acquisition circuit 120. The data acquisition circuit mayinclude a trans-impedance amplifier and an analog-to-digital (A/D)converter, which converts analog electrical signals from thephotodetectors 116, 122 into a sequence of digital samples. Thesedigital samples feed into the signal processing block 126 (describedfurther below with reference to FIG. 2 ). The digital processing block126 determines a composite fetal signal from mixed signals from thephotodetectors. The system then performs computations on the compositefetal signal produced from the mixed signals to determine a fetal bloodoxygenation level as follows. The signal processing block 126 performs afrequency domain and/or time domain filtering operation to removematernal signal components from mixed signals to produce a correspondingset of fetal signals, which are then combined using a weighted averagecomputation to derive a composite fetal signal. The system then performsa pulse oximetry computation on the composite fetal signal produced fromthe mixed signals to determine the fetal blood oxygenation level. Duringoperation of the IIFM illustrated in FIG. 1 , light sources 110 shinelight through maternal tissue and onto fetus 106, which is typicallylocated several centimeters below the skin. Arterial pulsations from thematernal and fetal heartbeats cause small changes in the tissue's lightabsorption, which cause slight changes in the diffuse reflectance whenmeasured at the surface of the maternal abdomen 104. By measuring thischange in the diffused light signal, oximetry calculations may beperformed to estimate the fetus blood oxygenation levels.

As shown in FIG. 1 , the IIFM system 100 may further include anElectronic Fetal Monitor (EFM) 128. The EFM 128 may be a system aspreviously known to monitor fetal conditions and uterine contractionsduring labor. The EFM may provide additional information to the IIFM 100such as the fetus heartrate (FHR), the maternal respiratory rate (MRR),the maternal heartrate (MHR) and uterine contractions as describedfurther below. The electronic fetal monitor provides maternal heartrate, fetus heart rate, uterine contraction, and possibly maternalrespiratory rate, signals that are used by the processing mechanism inconjunction with fetal pulse oximetry using TFO technology to present aunified indication of fetal health.

Implementations of the probe 102 may further include one or moretemperature sensors 130 and one or more motion sensors 132 as shown inFIG. 1 . The temperature sensor 130 may be placed in close proximity tothe light source 108 to monitor the maternal skin temperature where thetemperature may be the highest. In some implementations, the temperaturemay be monitored via near infrared radiation of the skin using thephotodetectors 116, 122. Alternatively, in other implementations thetemperature may not be sensed at all, but predicted using heatdissipation models and knowledge of the generated heat. The motionsensor 132 is connected to the data acquisition circuit 120. The motionsignal from the motion sensor to detect motion may then be connected tothe filter generator 222 in the signal processing block as shown in FIG.2 .

It is noted that FIG. 1 is a general representation of the physicalentities of the IIFM system and should not be considered to limit thatactual physical arrangement of the various entities of the system. Forexample, the drive circuit 112 and the data acquisition circuit 120 mayphysically reside in the probe 102 or in the monitor 114. For purposesof this descriptions, it is assumed that the drive circuit 112 and thedata acquisition circuit 120 reside in the probe 102. The monitor 114may include a display 134 for displaying information to a user asdescribed further below. The display 134 may also be the same display1022 as shown in FIG. 10 .

FIG. 2 illustrates a high-level diagram of the signal processing block124 introduced in FIG. 1 . The signal processing block 124 includes anoise reduction block 210 that receives a number of data channels,collectively referred to as channels 212, from the probe 102 (shown inFIG. 1 ). In this example, the data channels 212 include five channels,namely channels Ch1, Ch2, Ch3, Ch4 and Ch5. Data channels Ch1, Ch2, Ch3and Ch4 carry signals received from the photodetectors (such asphotodetectors 116, 122 in FIG. 1 ). These signals feed into the noisereduction block 210. The noise reduction block 210 may provide filteringin frequency domain and/or the time domain. For filtering in thefrequency, the data channels are input to the Fast Fourier Transformblock 214. The FFT block 214 performs FFT operations on the mixedsignals to compute corresponding frequency-domain representations of themixed signals. These frequency-domain representations pass through anMRR filter 216, which removes the maternal respiration component fromthe signal, a motion filter 218, which removes motion noise, and an MHRfilter 408, which removes the maternal heart rate component from thesignal. The MRR filter 216, the motion filter 218 and MHR filter 220 arecontrolled by a filter generator 222, which generates the filters basedon an MRR signal 224, uterine contractions signal 226 and an MHR signal228, which are received from external sensors such as from the EFM. TheFilter generator 222 may use uterine contractions, as measured by anexternal uterine contraction sensor, to generate a motion filter 218that removes signal artifacts induced by the uterine contractions. Theoutput of the photodetectors on the data channels may be directlyapplied to the MRR filter 216, or other filters, for filtering in thetime domain.

Referring again to FIG. 2 , the resulting filtered signals 230 from thenoise reduction block 210 feed through a data fusion component 232. Thedata fusion component 232 computes a weighted average of the filteredsignals based on a set of dynamically changing channel weights 234, toproduce an estimated FHR and a composite fetal signal 236. Although itis possible to use a weighted average function to compute the estimatedFHR and the composite fetal signal 234, the system is not limited tousing such a weighted average. In general, other types of data fusionfunctions can be used. The estimated FHR and composite fetal signal 236is output 238 from the signal processing block 124 and used as describedbelow. The dynamically changing channel weights 234 are produced byconsidering the prominence of FHR and its harmonics in the spectrum ofthe filtered signals 230, where a channel with higher signal energy atthe frequency components corresponding to the FHR and its harmonics willbe assigned a higher channel weight. Channel weights are dynamicallyadjusted as new data samples stream through the system.

The signal processing block 126 in FIG. 2 may further include a motiondetection block 240 that produces a motion signal 242 and a temperaturedetection block 244 that produces a skin temperature signal 246. Themotion detection block 240 may use an input signal 213 from one or moremotion sensors 132 in the probe 102. The system may determine movementof the probe and produce the motion signal 242. The motion signal 242 issent to the filter generator 222 to remove noise caused by the motion.Further, the temperature detection block 244 may input a signal 213 fromthe temperature sensor 130 that directly measures the temperature of theskin under the probe 102. Motion and temperature may also be estimatedfrom data on the data channels 212 from the photo detectors. Forexample, skin temperature may be sensed via near infrared radiation ofthe skin using the photodetectors 116, 122 using existing techniques toprocess data received from the photodetectors over data channels 212.

FIG. 3 illustrates a high-level diagram of the IIFM 100 as introduced inFIG. 1 . FIG. 3 provides a block diagram of the various functionalblocks of the IIFM 100 including the functions of the monitor 114. FIG.3 is not meant to indicate or limit the actual physical location of thedescribed entities. The IIFM 100 uses input from the probe 102 and theEFM 128 to safely estimate the fetus blood oxygenation levels asdescribed herein. The IIFM 100 includes the signal processing block 124described in FIG. 2 . The signal processing block 126 inputs signalsfrom the probe 102 via the data acquisition circuit 120 as describedabove. The signal processing block 126 outputs the estimated FHR andcomposite fetal signal 236 as described above. The estimated FHR andcomposite fetal signal 236 feeds into a fetal health monitor 310.Implementations of the system may include a fetal heart rate tracingmodule 314, which uses standard fetal heart rate tracing techniques, togenerate a separate indicator for the oxygenation of the fetus.Implementations may also include a historical and physiological contextmodule 320, a signal quality assessor 322, a skin temperature predictionmodule 324 and a safety manager 326. These various modules and entitiesare described further below.

The fetal health monitor 310 receives the estimated FHR signal 236 andanalyzes the energy of the estimated FHR signal 236 at the FHR frequencyto compute an estimated fetal blood oxygenation level 312 using awavelength-ratio-based technique for computing blood oxygenation. Thefetal health monitor 310 may also receive input from the historical andphysiological context module 320 and an assessed TFO signal qualitysignal 328 from the signal quality assessor 322. The fetal healthmonitor 310 further outputs a fetal health indicator 316 and aconfidence indicator 318 as described further below. The fetal healthindicator 316 indicates the level of risk for fetal hypoxia. Theconfidence indicator 318 indicates the level of confidence of the devicein its assessment of fetal health. Note that the system can use an FHRobtained through an external FHR sensor or an estimated FHR to determinethe estimated fetal blood oxygenation level (Estimated FSpO2) 312.

The fetal heart rate tracing module 314 produces a separate indicator ofthe oxygenation level of the fetus (sufficiently oxygenated,indeterminate, insufficiently oxygenated) based on the FHR obtainedthrough an external FHR sensor such as from the EFM 128. Fetal heartrate tracing module 314 also interprets FHR in the context of uterinecontractions obtained through the external uterine contraction sensoralso in the EFM 128. The system can use this separate indicator as anadditional factor while determining the blood oxygenation level of thefetus. This alternatively generated estimate can be used as a “sanitycheck” for the estimate produced using the estimated FHR and compositefetal signal from the signal processing block.

The IIFM 100 also includes a historical and physiological context module320. The historical and physiological context module 320 preventschanges in the estimated fetal blood oxygenation level that are deemedunlikely due to conflict with prior measurements or the physiologicalcontext. The historical and physiological context module 320 uses apiece wise-linear representation for previously determined fetal bloodoxygenation levels to compute an upper bound on how quickly bloodoxygenation levels can change. The bound is further refined byincorporating physiologically-plausible rate of oxygen exchange betweenthe fetus and mother. If a rate of change associated with a currentlydetermined fetal blood oxygenation level exceeds the upper bound, thesystem caps the currently determined fetal blood oxygenation level basedon the upper bound. Note that the output from historical andphysiological context module 320 can feed into fetal health monitor 310to provide yet another sanity check.

Referring again to FIG. 3 , some implementations of the IIFM 100 includea signal quality assessor 322 as shown in FIG. 3 . The signal qualityassessor 322 quantifies the quality of the acquired fetal signals(sometimes called photo-plethysmograph (PPG) waveforms) represented inthe composite fetal signal 236. The signal quality assessor 322 receivesinput from the signal processing block 124 and the safety manager 326 tooutput an assessed TFO signal quality 328 and a predicted TFO quality330.

Other implementations of the IIFM 100 also include a skin temperatureprediction module 324 as shown in FIG. 3 . The skin temperatureprediction module 324 may receive a skin temperature 332 from the signalprocessing block 124, and candidate parameters 334 and appliedparameters 336 from the safety manager to provide a current temperature338 and a predicted temperature 340 to the safety manager 326.

Implementations of the IIFM 100 also include a safety manager 326 asshown in FIG. 3 . The safety manager 326 receives the currenttemperature 338 and a predicted temperature 340 from the safety manager326. It also receives the assessed TFO signal quality 328 and thepredicted TFO quality 330 from the signal quality assessor 322, and theTFO dependency signal 342 from the fetal health monitor 320. The safetymanager 326 periodically (at a time period “T”) configures the TFOsystem applied parameters 336 to balance safety constraints and signalacquisition needs. The safety manager performs at least three basicfunctions. First, if FSpO2 does not strongly depend on TFO (FHR tracingoutputs category I or category III as described below), the safetymanager defers collection of TFO measurements. Second, if FSpO2 stronglydepends on TFO (FHR tracing outputs category II), the safety manager 326balances acquisition of high-quality TFO with safe temperature rise ofskin of the maternal abdomen. The safety manager balances quality signalacquisition with safe temperature rise via controlling the appliedparameters to the light source consisting of the drive current, the dutycycle, and TFO measurement scheduling (e.g., 1 second ON and 9 secondsOFF). To ensure Safety, if the skin temperature is projected to reachunsafe levels the safety manager 326 turns off TFO and may also generatean alarm for an operator. Third, the safety manager 326 providescandidate configuration parameters 334 and applied configurationparameters to the various blocks of the IIFM. The applied configurationparameters are provided to the drive circuit 112 to drive the lightsource 108. A detailed implementation of the safety manager is describedbelow with reference to FIG. 9 .

FIGS. 4A-4E illustrate various views of the probe 102 introduced in FIG.1 . FIG. 4A illustrates a bottom view of an implementation of a probe102 for estimating and monitoring fetal blood oxygen levels. In thisimplementation, the probe 102 includes a temperature sensor 130 in closeproximity to the light source 108. The light source 108 is shown with a“star” shape around the light source 108 to graphically indicate thelight source emits light. The probe 102 further includes a photodetector116 as a light sensor that is closer to the light source 108. Otherphotodetectors 122 are located further away from the light source 108.The probe 102 may further include a motion sensor 132. FIG. 4Billustrates a cross-sectional side view of the probe 102 shown in FIG.4A. In this view a heatsink 410 can be seen as described further below.

FIG. 4C illustrates a bottom view of another implementation of a probefor estimating and monitoring fetal blood oxygen levels. Thisimplementation has three light sources 108 for emitting light fromdifferent locations. The light sources 108 may emit light at the same ordifferent frequencies. The light sources 108 may be positioned such thatthey are equally distant from one or more of the photodetectors that arefurther from the light source, such as photodetectors 122.

FIG. 4D shows an enlarged view of an implementation of a light source110 in a probe 102. In this implementation, a heatsink 410 is in closeproximity and may be in contact with the backside of the light source110. This implementation further includes a number of convection andairflow channels 412 that help cool the light source and the skin incontact with the light source. The light source 108 may comprise one ormore LEDs.

FIG. 4E illustrates a bottom view of another implementation of a probe414 for estimating and monitoring fetal blood oxygen levels. In thisimplementations, light sources 110 are arranged in a pattern around thephotodetectors. In this example, the light sources 110 are centeredequally spaced from a center photodetector 416 around a circle 418.

FIG. 5 is a flowchart of an example implementation of the signal qualityassessor 322 of the IIFM 100 as shown in FIG. 3 . The signal qualityassessor 322 quantifies the quality of the acquired fetal signalsrepresented in the composite fetal signal 236. The signal qualityassessor 322 determines if there is a motion sensor present (step 510).The motion sensor may be a dedicated motion sensor on the probe or fromdata received on the data channels from the photo detectors as describedabove. If there is a sensor present (step 510=yes) then the signalquality assessor 322 determines if the motion is too vigorous (step512). If the motion is too vigorous (step 512=yes) then the signal isirreversibly corrupted and the signal quality assessor send a signal tothe safety manager (step 514). If the motion is not too vigorous (step512=no) then the signal quality assessor removes motion contribution tothe composite fetal signal using adaptive noise cancellation (step 516)and proceeds to step 518. Removing the motion contribution to thecomposite fetal signal using adaptive noise cancellation may includeadjusting inputs to the motion filter 218 via the filter generator 222described above.

Referring again to the flowchart of FIG. 5 , if there is no motionsensor present (step 510=no) or after removing any motion contribution(step 516), the signal quality assessor proceeds to steps 518 and 522.At step 518, the signal quality assessor quantifies the signal to noiseratio (SNR) of the composite fetal signal. The signal quality assessorthen produces an assessed signal quality (step 520). The assessed signalquality is provided to the fetal health monitor 310 and the safetymanager as shown in FIG. 3 . At step 522, the signal quality assessorcomputes change in the SNR using signal and noise models if thecandidate configuration parameters were to be applied. The signalquality assessor then produces a predicted signal quality (step 524).The predicted signal quality is provided to the safety manager as shownin FIG. 3 .

FIG. 6 is a flowchart of an example implementation of the skintemperature prediction module 324 in the IIFM 100 as shown in FIG. 3 .The skin temperature prediction module 324 begins with steps 610 and614. The skin temperature prediction module 324 gets candidateconfiguration parameters (step 610) and estimates the generated heatapplied over the period T using light source characteristics (step 612).Approximately concurrent to steps 610 and 612, the skin temperatureprediction module 324 determines if there are any temperature sensorsthat provide a measured skin temperature (step 614). If there are anytemperature sensors (step 614=yes) then the skin temperature predictionmodule 324 gets the current skin temperature (step 616). If there are notemperature sensors (step 614=no) then the skin temperature predictionmodule 324 determines if this is the first considered configuration(step 618). If this is the first considered configuration (step 618=yes)then the skin temperature prediction module 324 sets the initial skintemperature to 37 degrees C. (step 620). If this is not the firstconsidered configuration (step 618=no) then the skin temperatureprediction module 324 uses the predicted skin temperature at the end ofthe previous period as the initial temperature for the next period (step622). The skin temperature prediction module 324 also sends the currentskin temperature at the beginning of period T to the safety manager(step 628).

Referring again to the flowchart of FIG. 6 , at step 624 the skintemperature prediction module 324 receive an estimate of the generatedheat (from step 612) and an initial skin temperature (from step 616,step 620 or step 622) to simulate the change in temperature over periodT using a heat dissipation model. The skin temperature prediction module324 then sends a predicted skin temperature at the end of a period T tothe safety manager (step 626). The safety manager 326 uses theinformation received from the skin temperature prediction module 324, todetermine if the current candidate configuration parameters should beapplied to the probe (further discussed below). Where the configurationparameters used in step 624 are applied parameters (step 630=yes) thenthe skin temperature prediction module 324 proceeds to step 622 torecord the simulated skin temperature at the end of the current period T(derived in step 624), as the initial skin temperature at the end of thesubsequent period.

FIG. 7 is a flowchart of an example implementation of the fetal healthmonitor 310 in the IIFM 100 as shown in FIG. 3 . The fetal healthmonitor 310 begins with steps 712 and 718. The fetal health monitor 310inputs the assessed TFO signal quality from the signal quality assessor(step 712). The fetal health monitor 310 sets the sensor weight for thecomposite fetal signal received from the signal processing block 124 inproportion to the assessed signal quality (step 714). Where the sensorweight models the confidence in TFO sensor. The fetal health monitor 310then scales the “sensor weight” up or down in proportion to the level ofagreement between the FHR estimated by the TFO and by the conventionalEFM (step 716). The fetal health monitor 310 also inputs the estimatedFHR and the composite fetal signal (step 718) and computes FSpO2 (step720). At step 722, the fetal health monitor combines the computed FSpO2and the recent or historical FSpO2 in direct proportion to the sensorweight and in inverse proportion to the staleness to produce theestimated FSpO2 and the confidence indicator. The fetal health monitoralso generates the fetal health indicator using the estimated FSpO2 andthe FHR tracing category received from the FHR tracing module 314 (step730) as further described in reference to FIG. 8 . If the weight issignificant (step 724) and the estimated FSpO2 (output of 722) isphysiologically plausible (step 726) the fetal health monitor proceedsto step 728 to record the estimated FSpO2 (output of 722) in historicalFSpO2 and update its last update time (step 728).

FIGS. 8A and 8B represent an implementation of displaying the fetalhealth indicator produced by the fetal health monitor 310. In thisimplementation, the fetal health indicator integrates the estimatedFSpO2 and the industry fetal heart rate tracing classification obtainedfrom the EFM to present a unified indication of fetal health. Theunified indication of fetal health may be presented to healthprofessionals as shown in FIGS. 8A and 8B. The industry fetal heart rate(FHR) tracing classification provides three categories of FHR tracing.Category I FHR tracings are considered to be “normal” and are nottypically associated with fetal complications. Category II FHR tracingsare indeterminate. Category III FHR tracing are abnormal and haveassociated with adverse neurologic abnormalities. The fetal healthindicator displays one of three values using the colors green, orangeand red. The fetal health indicator colors are typically shown on thedisplay 134 to health professionals. The fetal health indicator color isdisplayed depending on the FHR tracing category, the estimated FSpO2value and confidence indicator from the fetal health monitor. FIG. 8Aprovides a table for the fetal health indicator where the confidenceindicator is strong. For example, if the estimated FSpO2 shows there issufficient oxygenation the fetal health indicator will indicate thecolor green if the category is I or II, and will indicate orange forcategory III. Similarly, FIG. 8B provides a table for the fetal healthindicator where the confidence indicator is weak.

FIG. 9 is a flowchart of an example implementation of the safety manager326 in the IIFM 100 as shown in FIG. 3 . The safety manager 326determines if the estimated FHR and composite fetal signal isirreversibly corrupted (step 910). If the signal is irreversiblycorrupted (step 910=yes) then the safety manager 326 turns off TFO byapplying an off configuration (step 926). If the signal is notirreversibly corrupted (step 910=no) then the safety manager 326determines if fetal health monitoring is strongly dependent on TFO (step912). As used herein, fetal health monitoring is strongly dependent onTFO when in category II and not strongly dependent on TFO when incategory I or III. If the safety manager 326 determines fetal healthmonitoring is not strongly dependent on TFO (step 912=no) then itproceeds to step 926. If the safety manager 326 determines fetal healthmonitoring is strongly dependent on TFO (step 912=yes) then itdetermines if this is the first period (step 914). If this is the firstperiod (step 914=yes) then the safety manger uses a defaultconfiguration as the candidate (step 916) and proceeds to step 920. Ifthis is not the first period (step 914=no) then the safety manger usesthe determined configuration in the previous period as the candidate(step 918) and proceeds to step 920. The safety manger inputs thecurrent and predicted skin temperatures and determines if they are safe(step 920). If the skin temperature being used, current or predicted, isnot safe (step 920=no) then it determines if the predicted skintemperature has been unsafe for a specified number of consecutive timeperiods (step 922). If the skin temperature has been unsafe for thespecified number of consecutive time periods (step 922=yes) then thesafety manager generates an alarm and shuts down TFO (step 924). If theskin temperature has not been unsafe for the specified number ofconsecutive time periods (step 922=no) then the safety manager turns offTFO by applying an off configuration (step 926).

Referring again to the flowchart in FIG. 9 , if the skin temperaturebeing used, current or predicted, is safe (step 920=yes) then the safetymanager applies the configuration parameters (step 928), which mayinclude using the parameters to drive the light source. The safetymanager 326 then assesses the signal quality for the applied parameters(step 930). At step 930, the safety manager assesses applied parametersand predicts for candidate parameters the signal quality to enable thesafety manager to adjust the parameters until a proper SNR isdetermined. Where there is a proper SNR the safety manager uses thedetermined configuration for the next period (step 932). If the signalquality is irreversibly corrupted, then the safety manager proceeds tostep 926 to turn off TFO.

The safety manager may iteratively adjust the candidate parameters basedon the SNR ratio in steps 934 to 948 to achieve a proper SNR ratiowithout generating excessive heat. Where the SNR is too high, the safetymanager 326 determines if the drive current is greater than the minimumallowed current (step 934). If the drive current is greater than theminimum allowed current (step 934=yes) then it reduces the drive current(step 936) and returns to step 930. If the drive current is not greaterthan the minimum allowed current (step 934=no) then it determines if theduty cycle is greater than the minimum allowed (step 938). If the dutycycle is greater than the minimum allowed (step 938=yes) then it reducesthe duty cycle (step 940) and returns to step 930. If the duty cycle isnot greater than the minimum allowed (step 938=no) then it uses thedetermined configuration for the next period (step 932). Where the SNRis too low, the safety manager 326 determines if the duty cycle is lessthan the maximum allowed (step 942). If the duty cycle is less than themaximum allowed (step 942=yes) then it increases the duty cycle (step944) and returns to step 930. If the duty cycle is not less than themaximum allowed (step 942=no) then it determines if the drive current isless than the maximum allowed (step 946). If the drive current is lessthan the maximum allowed (step 946=yes) then it increases the drivecurrent (step 948) and returns to step 930. If the drive current is notless than the maximum allowed (step 946=no) then it proceeds to step 926to turn off TFO.

FIG. 10 is a block diagram illustrating a computer system 1000. It willbe understood that logic blocks illustrated in FIG. 10 representfunctions, and do not necessarily correspond to particular hardware on aone-to-one basis. The computer system 1000 can include a data processor1002, instruction memory 1004, and a general purpose memory 1006,coupled by a bus 1008. The instruction memory 1004 can include atangible medium retrievably storing computer-readable instructions, thatwhen executed by the data processor 1002 cause the processor to performfunctions, processes, and operations according to one or more aspects ofthis disclosure.

The computer system 1000 can include a communications interface 1010configured to interface with a local network 1012 for accessing a localhost server 1014, and to communicate, for example, through an InternetService Provider (ISP) 1016 to the internet 1018, and access a remoteserver 1020. The computer system 1000 can also include a display 1022and a user interface or other input device 1024, either as separatedevices or combined, for example, as a touchscreen display.

Those of skill in the pertinent art will appreciate that information andsignals may be represented using any of a variety of differenttechnologies and techniques. For example, data, instructions, commands,information, signals, bits, symbols, and chips that may be referencedthroughout the above description may be represented by voltages,currents, electromagnetic waves, magnetic fields or particles, opticalfields or particles, or any combination thereof.

Further, those of skill in the art will appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

Various exemplary aspects and illustrative implementations thereof aredescribed in terms of sequences of actions performed, for example, byelements of a computing device. It will be recognized that such actionsdescribed can be performed by specific circuits (for example,application specific integrated circuits (ASICs)), by specificconfigurations of field programmable circuits (for example, fieldprogrammable gate arrays (FPGAs)), by program instructions beingexecuted by one or more processors, or by a combination of both.Additionally, such sequence of actions described herein can beconsidered to be implemented entirely within any form of computerreadable storage medium having stored therein a corresponding set ofcomputer instructions that upon execution would cause an associatedprocessor to perform the described herein. Thus, the various aspects ofcan be implemented in a number of different forms, all of which arecontemplated to be within the scope of the claimed subject matter. Inaddition, example forms and implementations for actions and operationsmay be described, for example, as “logic configured to” perform thedescribed action.

The methods, sequences and/or algorithms described in connection withthe embodiments disclosed herein may be embodied directly in hardware,in a software module executed by a processor, or in a combination of thetwo. A software module may reside in RAM memory, flash memory, ROMmemory, EPROM memory, EEPROM memory, registers, hard disk, a removabledisk, a CD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

Accordingly, implementations and practices according to the disclosedaspects can include a computer readable media embodying a method forde-duplication of a cache. Accordingly, the invention is not limited toillustrated examples and any means for performing the functionalitydescribed herein are included in embodiments of the invention.

While the foregoing disclosure shows illustrative embodiments of theinvention, it should be noted that various changes and modificationscould be made herein without departing from the scope of the inventionas defined by the appended claims. The functions, steps and/or actionsof the method claims in accordance with the embodiments of the inventiondescribed herein need not be performed in any particular order.Furthermore, although elements of the invention may be described orclaimed in the singular, the plural is contemplated unless limitation tothe singular is explicitly stated.

While the foregoing has described what are considered to be the bestmode and/or other examples, it is understood that various modificationsmay be made therein and that the subject matter disclosed herein may beimplemented in various forms and examples, and that the teachings may beapplied in numerous applications, only some of which have been describedherein.

Language is intended and should be interpreted to be as broad as isconsistent with the ordinary meaning of the language is used in thecontext of this disclosure, and to encompass all structural andfunctional equivalents. Except as stated immediately above, nothing thatis stated or illustrated is intended or should be interpreted to causededication of any component, step, feature, object, benefit, advantage,or equivalent to the public.

It will be understood that terms and expressions used herein have theordinary meaning accorded to such terms and expressions in theirrespective areas of inquiry and study except where specific meaningshave otherwise been set forth herein. Relational terms such as first andsecond and the like may be used solely to distinguish one entity oraction from another without necessarily requiring or implying any actualsuch relationship or order between such entities or actions. The terms“comprises,” “comprising,” and any other variation thereof, are intendedto cover a non-exclusive inclusion, such that a process, method,article, or apparatus that comprises a list of elements does not includeonly those elements but may include other elements not expressly listedor inherent to such process, method, article, or apparatus. An elementpreceded by “a” or “an” does not, without further constraints, precludethe existence of additional identical elements in the process, method,article, or apparatus that comprises the element.

In the foregoing Detailed Description, it can be seen that variousfeatures are grouped together in various examples for the purpose ofstreamlining the disclosure. This method of disclosure is not to beinterpreted as reflecting an intention that any summary point requiresmore features than it expressly recites.

What is claimed is:
 1. A method for safely determining a fetal bloodoxygenation level, comprising: activating at least one light source withat least two distinct wavelengths of light on an abdomen of a pregnantmammal to direct light into a maternal abdomen toward a fetus; receivinga set of mixed signals from a set of photodetectors positioned atdifferent locations on the maternal abdomen from reflected light of theat least two distinct wavelengths that traverses maternal tissue ormaternal and fetal tissue; producing a composite fetal signal from theset of mixed signals from the set of photodetectors; assessing a qualityof the composite fetal signal where the quality depends on asignal-to-noise ratio (SNR) of the composite fetal signal; determiningthe fetal blood oxygenation level by performing computations on thecomposite fetal signal produced from the mixed signals; and ensuring askin temperature of the maternal abdomen does not rise to unsafe levelsdue to the activation of the at least one light source using theassessed quality of the composite fetal signal to determine parametersapplied to the at least one light source to insure safe skin temperaturelevels.
 2. The method of claim 1 further comprising mounting the atleast one light source and the set of photodetectors in a probefashioned for placement on the maternal abdomen of the pregnant mammal,wherein the probe incorporates convection air-flow around the at leastone light source to remove heat.
 3. The method of claim 1 furthercomprising: providing a motion sensor in a probe; and filtering the setof mixed signals received from the set of photodetectors with data fromthe motion sensor.
 4. The method of claim 1 further comprisingdetermining a predicted skin temperature to optimize a probeconfiguration.
 5. The method of claim 4 further comprising predicting asignal quality of the composite fetal signal and using the predictedsignal quality to set the parameters for the probe configuration.
 6. Themethod of claim 1 wherein ensuring the skin temperature of the maternalabdomen does not rise to unsafe levels comprises adaptively reducingstrength of a drive current to the at least one light source.
 7. Themethod of claim 1 wherein ensuring the skin temperature of the maternalabdomen does not rise to unsafe levels comprises adaptively reducing aduty cycle of a drive current to the at least one light source.
 8. Themethod of claim 1 wherein ensuring the skin temperature of the maternalabdomen does not rise to unsafe levels comprises activating the lightsource less frequently to determine the fetal blood oxygenation level.9. The method of claim 1 wherein ensuring the skin temperature of thematernal abdomen does not rise to unsafe levels comprises keeping theskin temperature at or below 44, 43, 42, 41 or 40 degrees Celsius. 10.The method of claim 1 further comprising utilizing maternal heart rate,fetal heart rate, uterine contraction inputs from an electronic fetalmonitor and the determined fetal blood oxygenation level to present aunified indication of fetal health and a confidence indicator.
 11. Themethod of claim 1 further comprising: determining a predicted signalquality that is combined with the assessed quality of the compositesignal; and balancing a quality signal acquisition with safe temperaturerise via controlling parameters applied to the at least one lightsource.
 12. The method of claim 1 further comprising mounting the atleast one light source and the set of photodetectors in a probefashioned for placement on the maternal abdomen of the pregnant mammal,wherein the probe provides heat sinks to dissipate heat of the at leastone light source.
 13. A method for safely determining a fetal bloodoxygenation level, comprising: activating at least one light source withat least two distinct wavelengths of light in a probe on an abdomen of apregnant mammal to direct light into a maternal abdomen toward a fetus;receiving a set of mixed signals from a set of photodetectors positionedat different locations on the maternal abdomen from reflected light ofthe at least two distinct wavelengths that traverses maternal tissue ormaternal and fetal tissue; providing a motion sensor in the probe andfiltering the set of mixed signals received from the set ofphotodetectors with data from the motion sensor to produce a set ofmotion-filtered mixed signals; producing a composite fetal signal fromthe set of motion-filtered mixed signals; assessing a quality of thecomposite fetal signal; determining the fetal blood oxygenation level byperforming computations on the composite fetal signal produced from themixed signals; and ensuring a skin temperature of the maternal abdomendoes not rise to unsafe levels due to the activation of the at least onelight source using the assessed signal quality to determine parametersapplied to the at least one light source to insure safe skin temperaturelevels.
 14. The method of claim 13 further comprising mounting the atleast one light source and the set of photodetectors in a probefashioned for placement on the maternal abdomen of the pregnant mammal,wherein the probe incorporates convection air-flow around the at leastone light source to remove heat.
 15. The method of claim 13 furthercomprising determining a predicted skin temperature to optimize a probeconfiguration.
 16. The method of claim 15 further comprising predictinga signal quality of the composite fetal signal before a change to theprobe configuration is applied.
 17. The method of claim 13 furthercomprising: determining a predicted signal quality that is combined withthe assessed quality of the composite signal; and balancing a qualitysignal acquisition with safe temperature rise via controlling parametersapplied to the at least one light source.